This invention relates to apparatus and a process for the injection of metered amounts of pulverized material to a pressurized vessel. More particularly, this invention relates to apparatus and a process for the injection of metered amounts of pulverized material to a shaft furnace. The invention will be described in the embodiment of a blast furnace; but it is applicable to shaft furnaces in general and may be useful in any pressurized vessel which has a requirement for supply of pulverized material.
The apparatus and process of the present invention relates to the injection of metered amounts of pulverized materials by pneumatic means at a plurality of different points into a vessel which is under variable pressure. The pulverized material is injected through a plurality of pneumatic conveyance paths (pipes) supplied with a fluid comprised of the pulverized materials and the propellant (e.g., air). The propellant fluid is injected through a booster, while each of the pipes is provided with a variable delivery metering means for introducing metered amounts of pulverized materials into the fluid stream in each of the pipes.
The invention concerns more particularly, but is not limited to apparatus and a process for the injection of powdered coal into a blast furnace. The basic problem of the injection of solid fuels into a blast furnace has been solved by the process and the installation proposed in European Patent Application published under No. 21,222. The use of solid fuels, e.g., powdered coal or lignite, in blast furnaces, as a replacement for petroleum products, is of increasing interest in view of the fact that petroleum products are becoming increasingly expensive and increasingly scarce.
However, the use of pneumatic means for the injection of solid fuels into a blast furnace makes it necessary to control a certain number of variable, interrelated parameters, while observing certain starting or basic operating conditions. One of the starting or basic operating conditions is the injection of a predetermined amount by weight of fuels per unit of time into the blast furnace, for example, so many kilograms per hour, while ensuring regular distribution of this amount over the number of tuyeres through which the fuel is injected.
One of the main problems for successful coal injection is control of loss of pressure in the pneumatic conveyance paths. In order to effect pneumatic injection of pulverized coal, it is necessary to have pneumatic carriers, for example, pressurized air (which may be the mixing blast air as proposed in the European Patent published under No. 22,549), which not only effects delivery at a sufficient speed to avoid deposits or build-up of the coal in the conveying pipes and prevent backfiring, but in addition is at a sufficient pressure to overcome pressure losses in the conveying pipes and inject the fuel into the furnace against the action of the pressure prevailing in the furnace. Although the required speed for the pulverized coal can be determined by experimentation or by calculation, the same is not true of the pressure. Firstly, the pressure in the furnace is not constant; it undergoes fluctuations which in absolute value may be as high as one bar or more, and it is indispensable to take these fluctuations into account in order to effect the injection of solid fuels into the furnace against the action of that pressure and of these fluctuations. Secondly, the losses of pressure in the pneumatic conveying pipes are variable not only depending on the pressure in the furnace and the fluctuations of that pressure, but also depending on the length of these pipes, which obviously vary in length depending on which tuyere is connected to a given pipe. Considering that it is preferable to provide a separate conveying pipe for each tuyere and that the number of tuyeres in a blast furnace is about twenty, it will be apparent to and recognized by those skilled in the art that the problem posed in the control of the loss of pressure in the pipes and the correct metering of the solid fuel to be injected into the furnace is a problem of considerable and complex magnitude.
The aim of the present invention is to provide apparatus and an injection process which will achieve a solution to this complex problem.
In order to achieve this aim, the process of the present invention is characterized by (a) before the injection there is determined in each of the pipes a pressure measurement point situated in a position such that the loss of pressure .DELTA.P between that point and the point of injection of the pulverized material into the vessel will be the same for all the pipes and for the same charge of material in the pneumatic stream, (b) the values of these losses of pressure between these two points in each pipe are determined by theoretical or experimental methods for a selected amount of pulverized materials and for different pressures inside the vessels; (c) these values (i.e., pressure losses) are stored in a memory in the form of calibration data or curves; (d) during the injection of pulverized coal the losses of pressure between the previously determined points are continuously monitored for each of the pipes; (e) the operation of the metering means is controlled, on the basis of the calibration curves, in such a manner that when flucturations of pressure occur in the vessel the variations of losses of pressure caused by these fluctuations between the predetermined points are compensated by an increase or decrease of the charge of materials introduced by the metering means; and (f) that finally these losses of pressure between these determined points are maintained at a constant value corresponding to that determined by the total amount of material which it is desired to inject.
In other words, the loss of pressure, which previously was the core of the problem, is not only mastered but profitably utilized to control the metering means and regulate the pressure of the pneumatic fluid in accordance with the fluctuations of pressure in the vessel.
The necessary pressure of the pneumatic conveying fluid is provided by a booster (pump) associated with automatic flow regulators. The latter regulate the flow of the pneumatic fluid independently of its pressure, that is to say the pneumatic fluid passes through this regulator at the pressure necessary to entrain the pulverized material into the vessel against the action of the pressure prevailing in the vessel. Thus, according to the present invention, the pressure of the pneumatic fluid is automatically adapted to the amount of pulverized material delivered by the metering means into the pneumatic pipe, so that the loss of pressure between the desired measurement point in the pipe concerned and the point of injection into the vessel is maintained at a set value supplied by the calibration curves.
As a preferred embodiment, the process of the invention is used for the injection of powdered coal or lignite into a blast furnace. The features, characteristics and advantages of the invention will be described in detail with reference to one application to the preferred embodiment of a blast furnace, indicated below by way of example without constituting a limitation.